The use of heliostats in the field of concentrating solar power (CSP) is well established in the prior art. A typical CSP system includes at least one centralized tower and a plurality of heliostats corresponding to each centralized tower. The tower is centralized in the sense that the tower serves as the focal point onto which a corresponding plurality of heliostats collectively redirect and concentrate sunlight onto a target (also referred to as a focus or a receiver) associated with the tower. The concentration of sunlight at the target is therefore directly related to the number of heliostats associated with the target up to certain fundamental limits. This approach concentrates solar energy to very high levels, e.g., on the order of 1000× or more if desired. In practical application, many systems concentrate sunlight in a range from 50× to 5000×. The high concentration of solar energy is converted by the target into other useful forms of energy. One mode of practice converts the concentrated solar energy into heat to be used either directly or indirectly, such as by generating steam, to power electrical generators, industrial equipment, or the like.
In other modes of practice, the concentrated solar energy is converted directly into electricity through the use of any number of photovoltaic devices, also referred to as solar cells.
Heliostat field configurations can take various forms depending on the design of the target receiver and on the geometry constraints of the installation area. A common geometry arranges heliostats in concentric arcs with the target at the center of the effectual circle. In general, the target is located at a latitude that is closer to the equator relative to the heliostat field so as to improve the overall efficiency of the heliostat over the course of the year. It is noted that in some configurations it is possible for heliostats to completely encircle the target. Other possible configurations include various kinds of rectilinear grids of heliostats where there are definable rows and columns. Furthermore the number of heliostats may be the same in each arc/row or may vary.
In all practical cases of heliostat configurations there is a need to provide some quantity of spacing between individual and or groups of heliostats. Such spacing is at minimum required to ensure that heliostats can articulate in such a manner as to not collide with adjacent heliostats. In addition, there is a need to provide service access for routine maintenance such as cleaning, repair and replacement of failed components. Furthermore space between concentric arcs or rows of heliostats is advantageous in order to reduce the blocking caused by heliostats closer to the target. The amount of possible blocking for a given arc/row separation and mirror size increases with distance from the target. Conversely, to maintain a constant nominal optical area efficiency of a given heliostat, the spacing between arcs/rows must necessarily increase as a function of distance from the target.
In the case of ground mounted heliostat fields, there is generally sufficient area in which to optimize the configuration of the heliostats to meet the aforementioned spacing requirements. The application of heliostat fields to industrial rooftops for the purpose of generating industrial steam introduces additional configuration constraints. These are defined by the available rooftop geometry and a potentially increased need for access paths throughout the field in order to comply with various fire regulations and provide service access to other rooftop entities such as HVAC systems and the like.